DirectX collision test. - Is it worth to make your own engine?

I'm trying to learn game programming with Visual C++\DirectX. At the moment I can load XMeshes, move them around, turn the camera around them, make collision test for only a box world etc.(I made some short of classes for these thi开发者_StackOverflowngs)

Now, I made a 3D model for terrain and I want to make my character move on it. There is an hittest function on Flash AC3 that checks if objects touching each other. Actualy I don't expect that much easy way to make collision test on DirectX 8D, but I don't even have any idea about how to do that... So, If you can give me an idea about that or link for resources or anything to being learning: that would be fantastic...

Plus I want to ask. Which way I have to choose? Creating my own engine or using another one? If so can you suggest one of the engines I should use?(Actualy I just want to make collision test on sloping land, not using whole another Engine or Dark GDK.)

In short I want to learn collision test on sloping land...

Thank for giving your time...

You can use this: http://msdn.microsoft.com/en-us/library/bb172882(v=vs.85).aspx
There was a sample on it in some old DX9 SDK, but I can't seem to find it over the net...

For the second question: if you're learning, try to do everything yourself first. That will give you reliable understanding of how 3D-engines work, how to use them, what they can do, what they can't, etc. Then switch to existing solutions, as they will likely be somewhat better crafted :)